A method of fabricating a solar cell for solar photovoltaic power generation is as follows. First, after preparing a substrate, a back electrode layer is formed on the substrate and patterned by using a laser device, thereby forming a plurality of back electrodes.
Thereafter, a light absorbing layer, a buffer layer, and a high resistance buffer layer are sequentially formed on the back electrodes. Various schemes, such as a scheme of forming a Cu(In,Ga)Se2 (CIGS) based-light absorbing layer by simultaneously or separately evaporating Cu, In, Ga, and Se and a scheme of performing a selenization process after a metallic precursor film has been formed, have been extensively used in order to form the light absorbing layer. The energy band gap of the light absorbing layer is in the range of about 1 eV to about 1.8 eV.
Then, a buffer layer including cadmium sulfide (CdS) is formed on the light absorbing layer through a sputtering process. The energy bandgap of the buffer layer may be in the range of about 2.2 eV to about 2.4 eV. Thereafter, the high resistance buffer layer including zinc oxide (ZnO) is formed on the buffer layer through the sputtering process. The energy bandgap of the high resistance buffer layer is in the range of about 3.1 eV to about 3.3 eV.
Thereafter, a groove pattern may be formed in the light absorbing layer, the buffer layer, and the high resistance buffer layer.
Then, a transparent conductive material is laminated on the high resistance buffer layer, and is filled in the groove pattern. Therefore, a transparent electrode layer is formed on the high resistance buffer layer, and connection wires are formed in the groove pattern. A material constituting the transparent electrode layer and the connection wireless may include aluminum doped zinc oxide (AZO). The energy bandgap of the transparent electrode layer may be in the range of about 3.1 eV to about 3.3 eV.
Then, the groove pattern is formed in the transparent electrode layer, so that a plurality of solar cells may be formed. The transparent electrodes and the high resistance buffers correspond to each cell. The transparent electrodes and the high resistance buffers may be provided in the form of a stripe or a matrix.
The transparent electrodes and the back electrodes are misaligned with each other, so that the transparent electrodes are electrically connected to the back electrodes through the connection wires, respectively. Accordingly, the solar cells may be electrically connected to each other in series.
As described above, in order to convert the solar light into electrical energy, various solar cell apparatuses have been fabricated and used. One of the solar cell apparatuses is disclosed in Korean Unexamined Patent Publication No. 10-2008-0088744.
Meanwhile, it is crucial in such a solar cell how to reduce an energy bandgap difference between the buffer layer and the light absorbing layer to easily produce photovoltaic power. Therefore, studies for allowing the buffer layer and the light absorbing layer to have similar energy bandgaps have been actively performed.